It has recently been discovered and publicized that cathode ray tubes such as those widely employed in conventional television sets, instrument panels and currently proliferating in computer terminals emit low levels of harmful radiation. See J. N. Ott, Health and Light, Chapter 12, pg. 119 (1973). The non-visible radiation emitted by a cathode ray tube may include gamma radiation, x-ray radiation, ultraviolet, infrared radiation, radio waves, television waves and other microwaves. Human exposure to such radiation is undesirable and may result in deleterious biological effects.
In view of the above, it is the object of the present invention to provide an apparatus for removing harmful radiant emissions from the visible image producing radiation emitted by a cathode ray tube or other electronically activated television-like screen so that the visual image originating from such a source may be safely viewed.
In the past a variety of methods and devices have been used to selectively absorb or reflet both visible and non-visible radiation projected from electronically activated television-like screens. One of the earlier methods used to accomplish the above was the placement of a wavelength selective filter between the viewer and the screen. These filters transmitted only radiation of certain wavelengths while absorbing or reflecting all others. For example, U.S. Pat. No. 2,470,666 discloses a light shielding enclosure for the screen-end of a cathode ray tube used for displaying various wave configurations. Although this patent discloses the basic concept of selectively filtering radiation of different wavelengths, it does so only within the context of selecting one visible light ray from another visible light ray, i.e., blue from amber. The principle of selection is that of passing radiant energy through a filter; the radiation received by the viewer is still beamed directly at the viewer, as is the case with the following two patents.
U.S. Pat. No. 2,690,554, like the '666 patent discussed above, discloses a transparent filter for use with a cathode ray tube. The disclosed filter is adapted to selectively filter out ultraviolet radiation using a silica-soda-potash-lime glass containing therein small quantities of cerium which renders the glass absorbent to practically all radiation having a wavelength below 360 angstroms.
U.S. Pat. No. 2,655,452 discloses a glass composition adapted for use in the construction of the screen end of a cathode ray tube and more particularly a television picture tube. The disclosed glass is capable of absorbing harmful x-ray and ultraviolet rays resulting from the bombardment of the fluorescent coating on the inside face of the screen by an electron beam. In this patent, the glass acts as the filter.
U.S. Pat. No. 3,473,944 discloses a radiation-reflective sheet consisting of a glass panel coated on opposite sides with films comprising varying amounts of antimony oxide and tin. The panel is adapted to reflect heat as well as substantial amounts of radiation throughout the visible spectrum while at the same time permitting objects viewed therethrough to be seen without distortion of color.
U.S. Pat. No. 3,645,600 discloses a heat absorbing reflector comprising a metallic substrate having positioned thereon an anti-reflection coating and multilayer interference coating. This device is adapted to reflect generally all wavelengths of radiation within the visible spectrum while absorbing substantially all wavelengths of heat radiation (i.e., electromagnetic radiation in the wavelength range beyond 0.7 microns).
Unlike the wavelength selective filters discussed above, the apparatus of the present invention selectively removes harmful radiation from the image producing radiation transmitted by a cathode ray tube or other electronically activated television-like screen, by selectively reflecting visible radiation to the eye of the observer, while selectively absorbing the non-visible radiation emitted by the cathode ray tube or other electronic image originating source, and by selectively altering the path travelled by the non-visible radiation transmitted by the image originating source such that it is directed out of the line of sight of the observer.
The prior art also discloses various devices employing two reflective surfaces wherein the first reflective surface receives the reflected image from a cathode ray tube and reflects the image to the second reflective surface from which the observer views the image. See U.S. Pat. Nos. 2,438,256, 3,291,906, 2,165,078, and 2,234,227. However, unlike the apparatus of the present invention, the devices disclosed by the abovelisted patents do not employ means for selectively removing harmful radiation from the visible radiation originating from the cathode ray tube.